A method for operating a data storage device is provided, and the method comprises the steps: enqueuing requests for a nonvolatile memory device, received from a host device, in a first queue; determining whether a starvation time of a request which is not enqueued in a second queue and has a relatively low priority, among the requests queued in the first queue is reaching to a predetermined response time; and enqueuing, based on a determination result, any one between the request which has the low priority and a request which is not enqueued in the second queue and has a high priority among the requests queued in the first queue, in the second queues.